Since cities and towns first became congested with people and vehicles, there have been problems in getting emergency vehicles from one place to another in a reasonable time.
With the development of signals sent by wire and later signals sent by radio waves, efforts have been made to utilize this capability to aid in the movement of emergency vehicles through congested areas. As early as 1918 remote signalling devices were used to control "Stop" and "Move" intersection signs. Later light signals were used to control stop lights to allow emergency vehicles to go through intersections with all other traffic stopped. Radio signals were used to do the same thing. Even later computer programs have been used to preempt the usual operation of traffic lights along a predetermined vehicle route. None of these various traffic control means, however, have been able to allow the emergency vehicle crew to choose alternate routes to their destination which are either accepted or rejected until a satisfactory route is established.